1. Technical Field
This invention relates to an electronic control device performing a fuel control operation, an ignition control operation, and so forth for an internal combustion engine which uses a fuel obtained by mixing an oxygenated compound such as methanol, ethanol and MTBE (methyl tertiary butyl ether) with a petroleum refined fuel such as gasoline.
2. Background Art
Recently, in the United States of America and various European countries, in order to decrease the consumption of petroleum and to reduce the air pollution by exhaust gas from motor vehicles, a fuel prepared by mixing an oxygenated compound such as alcohol and ether with gasoline has been employed for motor vehicles. If such an oxygenated compound mixed gasoline is used, as it is, for an internal combustion engine matched with a gasoline fuel, then the engine suffers from the following difficulties: That is, methanol is appreciably different in theoretical air-fuel ratio from gasoline, about 6 to 15, and the former is larger in octane value that the latter, and the distillation characteristic depends on the methanol content. Hence, the operation of the engine is not satisfactory, and serious problems to be solved are involved in the driving characteristic of the engine and in the quantity of hazardous components exhausted therefrom. Thus, in controlling the operation of the engine, it is essential to detect the methanol content of the methanol mixed fuel.
An electronic control device for an internal combustion engine using an alcohol mixed fuel as an oxygenated compound mixed fuel has been disclosed by Japanese Patent Application (OPI) No. 98540/1981 or 51920/1982 (the term "OPI" as used herein means an "unexamined published application"). The conventional electronic control device is designed as follows: An alcohol content sensor is provided in the pipe through which an alcohol mixed fuel is supplied to the engine. That is, by detecting the dielectric constant (Japanese Patent Application (OPI) No. 98540/1981) or refractive index (Japanese Patent Application (OPI) No. 51920/1982) of the alcohol mixed fuel passing through it, the alcohol content of the alcohol mixed fuel is detected. The alcohol content thus detected is utilized to adjust the supply of the fuel thereby to control the air-fuel ratio, and to correct the ignition advance angle thereby to control the ignition timing.
That is, the fuel injection quantity is increased in proportion to the alcohol content to maintain the air-fuel ratio satisfactory. And, since alcohol is high in combustion speed, the ignition timing is, in general, delayed in proportion to the alcohol content. Furthermore, in the case of an alcohol mixed fuel, alcohol is lower in volatility than gasoline, and therefore the engine is unsatisfactory in starting characteristic when the temperature of the engine is in a range of low and middle temperatures. Hence, in the case when the temperature of the engine is in that range, especially at the start of the engine and immediately after it, control is made according to the alcohol content.
However, the above-described conventional electronic control device is disadvantageous in the following points: With the device, the operation of the engine is controlled only according to an alcohol content. Hence, in the case when the nature of gasoline mixed with alcohol changes, then the driving characteristic of the engine, and the quantity of hazardous components exhausted therefrom are adversely affected. That is, the volatility of an alcohol mixed fuel affecting the starting characteristic of an internal combustion engine depends not only on the alcohol content but also the volatility of the gasoline. The volatility of gasoline depends on the nature of distillation thereof. Under the condition that the temperature of the engine is in the above-described range of low and middle temperatures, the starting characteristic of the engine using a heavy gasoline low in volatility is lower than that of the engine using a light gasoline high in volatility.
On the other hand, the dielectric constant of an alcohol mixed fuel depends on the alcohol content, but it scarcely depends on whether the gasoline is a heavy one or whether it is a light one. On the other hand, the refractive index of the alcohol mixed fuel depends both on the alcohol content and the nature of the gasoline, but it is substantially free from whether the gasoline is a heavy one or whether it is light one. With a heavy gasoline low in volatility, or with a mixed fuel prepared by mixing alcohol with the heavy gasoline, the driving characteristic of the engine, and the amount of hazardous components exhausted therefrom are adversely affected, and at worst the engine cannot be started.